1. Field of the Invention
The present invention relates to a backlight module, and particularly to one used in a liquid crystal display (LCD).
2. Discussion of the Related Art
In a backlight type LCD, light beams are applied to a display member from the rear of the display member. Portions of the display member selectively allow transmission of the light beams therethrough, while other portions are opaque and prevent transmission of the light beams. The transmitted light beams are seen by an observer as displayed information. Important characteristics of the LCD include its long working lifetime, low power consumption, and brightness and uniformity of the emitted light rays. High brightness and uniform illumination help an LCD provide good display performance.
Referring to FIG. 6, a conventional backlight module 1 comprises a light source group 11 and a light guide plate 12. The light source group 11 comprises several light emitting diodes (LEDs) (not labeled). The light guide plate 12 has a light input surface 121 and a light output surface 122. Because each LED emits light over a certain range of angles, a scope of illumination 13 of the light source group 11 is the sum of the contributions of each LED's output light. Nevertheless, the illumination scope generally cannot cover the whole light guide plate 12. The hatched areas 14 in FIG. 6 show parts of the light guide plate 12 that are not illuminated. These parts are known as ‘dark zones.’ The existence of dark zones diminishes the performance of the backlight module 1.
Referring to FIG. 7 and FIG. 8, China Patent No. 98206129 issued on Nov. 10, 1999 discloses another kind of backlight module 2. The backlight module 2 comprises a light source group 21 and a light guide plate 22. The light source group 21 comprises three light emitting diodes (LEDs, not labeled), and the light guide plate 22 has a light input surface 221 and a light output surface 222. The light input surface 221 defines three U-shaped grooves, each matching with a corresponding LED. Thus each LED faces a concave surface of the corresponding U-shaped groove, and light beams passing through the concave surface cover a larger area of the light guide plate 22 in comparison with the above-described backlight module 1. Even so, the backlight module 2 still exhibits dark zones 24.
It is desired to provide a backlight system and a light guide plate used therein which overcome the above-described problems.